The present invention relates to polarized signal receiver waveguides in general, or so-called "feedhorns", as used in dish antennas for TVRO (television receive only) systems, and more particularly to a single-piece polarized signal receiving and signal transmitting waveguide.
The RF signals transmitted by communication satellite transponders consist of two linearly polarized signals, rotated 90.degree. from each other. The linearly polarized signals reflected by the dish are received through the open end of a feedhorn, installed at the focus of the dish and comprising a waveguide of circular cross section. Only one of the two polarized signals is received, the other signal being reflected out of the feedhorn. The detected signal is fed through a second waveguide, generally a waveguide having rectangular cross-section, whose axis is conventionally disposed at 90.degree. to the axis of the feedhorn waveguide, and which feeds the detected signal to a low-noise amplifier (LNA).
Various antenna probe arrangements may be used for receiving one of the polarized signals in the feedhorn circular waveguide and for launching, or retransmitting the detected signal into the rectangular waveguide. Generally, the probe comprises a receiver portion disposed in the circular waveguide, and a signal launch or transmitter portion disposed in the rectangular waveguide, the probe being supported by a rotatable dielectric rod driven by a servomotor mounted on the waveguide assembly. The launch or transmitter portion of the probe has its axis aligned with the axis of the circular waveguide and with the axis of the dielectric rod, such as to remain constantly perpendicular to the axis of the rectangular waveguide during rotation of the probe. The probe receiver portion has its longitudinal axis perpendicular to the axis of rotation such as to rotate between the two orthogonally polarized signals in the circular waveguide. By rotation to a desired position, one polarized signal is received and the other is reflected. The received signal is conducted by the transmission line portion of the probe through the rear wall of the circular waveguide and is launched or retransmitted into the rectangular waveguide by the probe launch or transmitter portion.
The circular waveguide and the rectangular waveguide are conventionally made of separate elements, usually separate castings of, preferably, aluminum alloy. The two castings are assembled together, usually by providing one of the waveguides, for example the rectangular waveguide, with a flange which is bolted to the rear end of the circular waveguide, the rectangular waveguide being provided with a circular recess in which projects a correspondingly cylindrical end portion of the circular waveguide. Such an assembly is relatively fragile, causes power losses and the introduction of noise in the signal received in the circular waveguide and launched or retransmitted in the rectangular waveguide.
As the waveguide assembly is installed in an outdoor TVRO dish antenna, the assembly is exposed to inclement weather, such as rain or snow, dust and high wind, and to atmospheric pollution, all adverse conditions that may cause rapid deterioration, corrosion of the metallic surfaces and loosening of the joint between the waveguides. There results further deterioration of the relatively low level ultra-high frequency signals captured by the antenna system.
The present invention is an improvement upon the prior art polarized signal feedhorn waveguides and probes.